A semiconductor chip may be electrically connected to a bonding pad formed on a printed circuit board through a wire.
FIG. 1 is a cross-sectional view showing a known semiconductor chip 20 attached to a printed circuit board 10.
Referring to FIG. 1, the semiconductor chip 20 is connected to the printed circuit board 10 by a wire 18. The wire 18 is bonded to a bonding pad 14 formed on the printed circuit board 10. The bonding pad 14 is electrically connected with a wiring (not shown) formed on the printed circuit board 10. Although gold is preferably used as a material for the bonding pad 14, a copper layer plated with gold has been used for reducing the manufacturing cost. However, when copper is in direct contact with gold, copper may diffuse into the gold, thereby weakening the adhesivity between the wire 18 and the bonding pad 14 or causing galvanic corrosion.
One known method to attempt to avoid copper diffusion into gold is described in connection with FIG. 2, which is an enlarged sectional view of the bonding pad 14 of FIG. 1. In the bonding pad 14, a nickel layer 14b serving as a diffusion barrier film—is formed between a copper layer 14a and a gold layer 14c to prevent the direct contact between them. While the nickel layer 14b provides a reduction in copper diffusion, the additional cost incurred through the use of nickel makes this approach undesirable.
What is needed, therefore, is a bonding structure that overcomes at least the shortcomings described above.